Acoustic deterrence

Abstract

A method and system of deterring mammals is disclosed involving incurring an acoustic startle response comprising the steps of selecting a target order, family, genus or species to be deterred, selecting a received level that is a predetermined level above a representative hearing threshold of the targeted mammals, and, taking transmission loss into account, transmitting an acoustic signal at a source level required to create the selected received level at a predetermined distance from the transmission point. The acoustic signal may comprise frequency components at which the aural sensitivity of the targeted mammals is greater than that of selected other animals, preventing the disturbance of the selected other animals while deterring the targeted mammals. In addition, a secondary conditioning sound may be played prior to the main acoustic signal to condition the mammals to avoid the main stimulus. Furthermore, using the same steps, an aversive stimulus may be played that elicits an avoidance without a startle reflex. The characteristics of these aversive sounds are those found to be unpleasant to humans. Accordingly, the aversive sound is selected to have one or more of the following psychophysical features: high roughness; low tonality; high loudness; high sharpness.

1. A method of deterring mammals comprising configuring an acoustic deterrent system to emit an acoustic signal, said acoustic signal having a level sufficiently high, and rise time sufficiently short to elicit an acoustic startle response reflex in said mammals,
 wherein incurring an acoustic startle response comprises the steps of: 
 selecting a target order, family, genus or species of mammals to be deterred; 
 selecting a received level at a predetermined level above a representative hearing threshold of the targeted mammals; 
 transmitting an acoustic signal from a transmission point at a source level required, taking into account transmission loss, to create the selected received level at a predetermined distance from the transmission point, and 
 wherein a secondary conditioning sound is made to condition the mammals to avoid the main stimulus. 
 
     
     
       2. A method as claimed in  claim 1 , wherein the predetermined level is between 90 and 125 dB above the representative hearing threshold. 
     
     
       3. A method as claimed in  claim 1 , wherein the acoustic signal has a duration about as long as the acoustic integration time specific to the targeted mammals auditory system. 
     
     
       4. A method as claimed in  claim 1 , wherein the acoustic signal has a duration of less than 200 milliseconds (ms). 
     
     
       5. A method as claimed in  claim 1 , wherein the acoustic signal has a rise time of less than 20 ms. 
     
     
       6. A method as claimed in  claim 1 , wherein the acoustic signal is as broadband as possible within the designated frequency range. 
     
     
       7. A method as claimed in  claim 1 , wherein the acoustic signal comprises frequency components at which the aural sensitivity of the targeted mammals is greater than that of selected other animals. 
     
     
       8. A method as claimed  claim 1 , wherein the acoustic signal uses frequency band between 500 Hz and 2 kHz for the deterrence of seals or other pinnipeds. 
     
     
       9. A method as claimed in  claim 1 , wherein the mammals to be deterred comprise sea mammals including pinnipeds, most preferably seals; or cetaceans. 
     
     
       10. A method as claimed in  claim 1 , wherein the mammals to be deterred comprise land mammals. 
     
     
       11. A method as claimed in  claim 1 , wherein the secondary conditioning sound comprises a sound of centre frequency 1 KHz, modulation rate 250 Hz and duration 1.2 seconds with two modulation cycles. 
     
     
       12. A method as claimed in  claim 1 , wherein the conditioning sound is played between 500 ms and 5 s before the main acoustic signals on selected occasions. 
     
     
       13. A method as claimed in  claim 1 , wherein the acoustic deterrent system comprises a signal transducer arranged to transmit said acoustic signal. 
     
     
       14. A method as claimed in  claim 1 , wherein the acoustic deterrent system comprises a control unit, a power source, amplifier and arranged to produce said acoustic signal. 
     
     
       15. A method as claimed in  claim 14 , wherein the acoustic deterrent system includes a control unit that operates under the control of control software executable on a computer. 
     
     
       16. A method as claimed in  claim 15 , wherein the control software is stored on a computer readable medium. 
     
     
       17. A method as claimed in  claim 1  wherein the predetermined level above the representative hearing threshold is between 95 and 125 dB re 1 μPa and the rise time of the sound is 1-20 ms. 
     
     
       18. A method of deterring marine mammals comprising configuring an acoustic deterrent system to emit an acoustic signal, said acoustic signal comprising an aversive sound whose characteristics are chosen based on characteristics that are unpleasant to humans, wherein the aversive sound is selected to have one or more of the following psychophysical features: low tonality; high loudness; high sharpness, and wherein a frequency modulation with a modulation frequency of about 70 Hz is applied to a carrier signal. 
     
     
       19. A method as claimed in  claim 18 , wherein the frequency modulation has a modulation depth of between 10 and 150%, preferably 50% of the centre frequency of the carrier signal. 
     
     
       20. A method as claimed in  claim 18 , wherein the aversive sound has a sound pressure level of at least 70 dB above the hearing threshold of the targeted mammals, most preferably at least 80 dB above the hearing threshold of the targeted mammals. 
     
     
       21. A method as claimed in  claim 18 , wherein the aversive sound is of a complex form and comprises partials that fall within 25% of the critical bandwidth of the hearing system of the targeted mammals. 
     
     
       22. A method as claimed in  claim 18 , wherein when cetaceans are to be deterred, the acoustic signals are close, to the upper frequency edge of the hearing range in order to increase sharpness. 
     
     
       23. A method as claimed in  claim 18 , wherein the acoustic signal is as broadband as possible within the selected frequency band in order to increase loudness without increasing the actual sound pressure level. 
     
     
       24. A method as claimed  claim 18 , wherein the aversive sound comprises frequency components at which the aural sensitivity of the targeted mammals is greater than that of selected other animals. 
     
     
       25. A method as claimed in  claim 18 , wherein the acoustic signal comprises one or more frequency components between 500 Hz and 2 kHz for the deterrence of seals or other pinnipeds. 
     
     
       26. A method as claimed in  claim 18 , wherein sound exposure time and level are determined such that the resulting sound does not cause a temporary or permanent hearing threshold shift in target and non-target species. 
     
     
       27. A method as claimed in  claim 25 , wherein the sound exposure level is 120 dB re 1 μPa 2 s −1  above the hearing threshold of the targeted mammals.